Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may include both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles and may sometimes be referred to as soot.
Due to increased environmental concerns, among other things, exhaust emission standards may have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine.
Engine manufacturers have employed exhaust treatment devices called particulate traps to remove the particulate matter from the exhaust flow of an engine. A particulate trap may include a filter designed to trap particulate matter. The use of the particulate trap for extended periods of time, however, may enable particulate matter to accumulate on the filter, thereby causing damage to the filter and/or a decline in engine performance.
One method of restoring the performance of a particulate trap may include regeneration. Regeneration of a particulate trap filter system may be accomplished by thermal regeneration, which may include increasing the temperature of the filter and the trapped particulate matter above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter and regenerating the filter system. This increase in temperature may be effectuated by various means. For example, some systems employ a heating element (e.g., an electric heating element) to directly heat one or more portions of the particulate trap (e.g., the filter material or the external housing). Other systems have been configured to heat the exhaust gases upstream from the particulate trap, allowing the flow of the heated gases through the particulate trap to transfer heat to the particulate trap. For example, some systems may alter one or more engine operating parameters, such as air/fuel mixture, to produce exhaust gases with an elevated temperature. Running an engine with a “rich” air/fuel mixture can elevate exhaust gas temperature. Other systems heat the exhaust gases upstream from the particulate trap, with the use of a burner that creates a flame within the exhaust conduit leading to the particulate trap.
Some systems may be configured to initiate regeneration in response to one or more trigger conditions that may be indicative of significant accumulation of particulate matter in a particulate trap. For example, some systems may include one or more pressure sensors configured to measure “backpressure” in an exhaust system (i.e., pressure in the exhaust system upstream from a particulate trap). Such systems may be configured to initiate regeneration upon detection of a backpressure above a predetermined level, which may indicate significant blockage of exhaust flow due to accumulation of particulate matter in the filter.
Other systems have been developed to measure, estimate, or otherwise detect the amount of particulate matter that has accumulated on a particulate filter. For example, U.S. Pat. No. 5,497,099 (the '099 patent), issued to Walton, describes an apparatus for detecting the accumulation of particulate material on a filter. The apparatus includes an amplitude modulation radio frequency (RF) generator, a transmitter, output and input antennas, and a monitor for measuring the transmission loss through at least a portion of the filter medium.
Although the system of the '099 patent may detect soot in a filter medium, it may use a modulated radio frequency signal. For example, the '099 patent discloses an amplitude modulation (AM) radio frequency generator. Use of modulated radio frequency signals, such as AM, may require additional components and may lead to a more complicated and/or costly system.
The disclosed system is directed to one or more improvements in existing particulate matter detection systems.